FIG. 13 shows the configuration of a rotation detector used in related art. A rotation detector 1 includes a stator 2, which is a fixed member, and a rotor 3, which is a rotating member rotatable relative to the stator 2, as shown in FIG. 13. The stator 2 is made of a magnetic material and has a stator coil 2b provided via an insulating sheet 2a on the surface facing the rotor 3. The rotor 3 is also made of a magnetic material and has a rotor coil 3b provided via an insulating sheet 3a on the surface facing the stator 2. Each of the stator coil 2b and the rotor coil 3b is formed of a copper foil and formed in a coil pattern having a rectangular waveform.
The rotation detector 1 further includes a rotary transformer 4 for exciting the rotor coil 3b. The rotary transformer 4 is formed of a transformer coil 4b, which is connected to the rotor coil 3b, and a transformer coil 4a, which is located in an inner circumferential portion of the stator 2 and supplies the coil 4b with an excitation signal in a noncontact manner. In the configuration described above, when the excitation signal is supplied to the rotor coil 3b via the rotary transformer 4, the stator coil 2b outputs a detection signal as the rotor 3 rotates.